Office for Nuclear Regulation

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Compliance inspection of Licence Condition 19

Executive summary

Purpose of Intervention

In accordance with the Office for Nuclear Regulation’s (ONR’s) Hinkley Point C HPC)  Construction Inspection Plan, ONR performs a series of planned compliance inspections of identified licence conditions, to ensure that NNB Generation Company (HPC) Ltd (NNB GenCo), is proportionately and adequately developing and implementing its licence compliance arrangements commensurate to the current stage of the project.

This intervention included a routine licence condition inspection carried out to assess NNB GenCo (HPC)’s compliance with licence condition 19; Construction or installation of new plant focusing on the adequacy of NNB and its contractors control of the fabrication of the inner containment liner to ensure it meets NNB’s design and quality requirements. The inner containment liner is a safety significant component which in conjunction with the concrete containment structure contributes to the confinement of radioactive materials in operation and certain fault conditions.

In addition I held a number of information sharing meetings and attended the Hinkley Point C community forum.

Interventions Carried Out by ONR

LC19 requires that “Where the licensee proposes to construct or install any new plant which may affect safety the licensee shall make and implement adequate arrangements to control the construction or installation.”

ONR carried out the following LC 19; Construction or installation of new plant inspection:

.The following guidance was used in this intervention:

NS-INSP-GD-019 Revision 5 “LC19 – Construction or Installation of New Plant”

Explanation of Judgement if Safety System Not Judged to be Adequate

N/A as this was not a safety systems inspection.

Key Findings, Inspector's Opinions and Reasons for Judgements Made

LC19 – Inner containment welding

NNB is enacting appropriate levels of control regarding the commencement of inner containment liner welding to ensure that its requirements are met prior to the start of safety significant welding operations. This had resulted in welding operations not having commenced at the time of the intervention.

NNB/Bylor (NNB’s main civil works contractor) and Tissot (Bylor’s tier 2 contractor for the production of the containment liner)  have taken significant learning from similar fabrication activities at the Flamanville 3 EPR and as a result have put in place a number of improvements which should help ensure significantly improved performance of containment liner welding operations at HPC.
Tissot’s fabrication compound was found to tidy with appropriate control of weld consumables and the staff interviewed could articulate a good understanding of the key parameters contributing to high quality welding.

NNB has assigned the containment liner a class 1 safety function however the component has been designed in accordance with its civils approach and at the time of the inspection it was unclear how this approach ensures that the surveillance requirements for mechanical components designed as part of civil structures are commensurate to similar classified systems designed using NNB’s mechanical system approach.

Whilst Tissot has put in place a number of arrangements to ensure that non-English speakers are provided with appropriate information, the supervisory ratio it has implemented is not currently in accordance with NNB’s stated generic expectations.

Conclusion of Intervention

LC19 – Inner Containment Welding

Overall I judge that overall an inspection rating of GREEN (No formal action) is appropriate for licence condition 19; Construction or installation of new plant in relation to inner containment welding operations. This is because overall I found NNB GenCo and its contractors have in general put in place appropriate arrangements to ensure the control of inner containment welding with evidence of significant learning from experience from Flamanville 3 (noting that welding had yet to commence and some documentation was not available at the time of the inspection).

Whilst overall I judge that a GREEN rating is appropriate, I have raised two level 4 regulatory issues which I consider should be addressed promptly, one regarding implementation of supervisory ratios for non-English speaking personnel and one requiring NNB to demonstrate how surveillance requirements for mechanical components designed as part of civil structures are derived to ensure that such components receive a level of oversight and surveillance commensurate to mechanical system designed components.